1. Field of the Invention
The present invention relates, in general, to a System-in-Package (SiP) having reduced influence between a conductor and an antenna, and a method of designing the SiP, and, more particularly, to a SiP, which can reduce the influence of a planar conductor on the operating characteristics of an antenna in a SiP in which the antenna is integrated, and a method of designing the SiP.
2. Description of the Related Art
Recently, in mobile devices, such as mobile phones and Personal Digital Assistants (PDAs), technology for System-in-Package (SiP), in which various systems and passive devices are implemented in the form of a single package to realize the small size of the mobile devices, and in which an antenna for data transmission/reception is also integrated in the package, has been variously used.
For example, a Radio-Frequency Identification (RFID) system has been widely used for traffic cards, entrance control cards, etc. Recently, a mobile RFID system has been standardized, and the necessity to mount an RFID reader in a mobile device has increased, so that the importance of SiP technology has gradually increased in order to reduce the size of a large RFID reader.
FIG. 1 is a view showing the structure of a conventional RFID reader package.
As shown in FIG. 1, an RFID reader package is typically implemented in a four-layer structure. That is, the RFID reader package is composed of a top layer 102, on which a plurality of chips and passive devices is mounted, a bottom layer 104 connected to ball or lead frames required to mount the package on a test board, a power layer 106 for supplying power to the chips and devices in the package, and a ground layer 108 for grounding.
In typical cases, as shown in FIG. 1, conductors for supplying power and providing ground are formed both on the power layer 106 and on the ground layer 108 in the shape of planes, rather than lines, in order to realize power integrity.
The term ‘power integrity’ means the pure and stable supply of the power and ground to prevent noise from occurring in the power and the ground. In order to stably supply power and provide ground, which are Direct Current (DC) voltages, and to decrease DC loss, it is preferable that a power conductor and a ground conductor be implemented in the shape of small planes, having a low impedance value, rather than the shape of lines, having a high impedance value, from the standpoint of power integrity.
FIGS. 2A and 2B are views showing an example in which a conventional RFID reader, in which an antenna is also integrated, is implemented in the form of a SiP.
FIG. 2A is a plan view of an RFID reader SiP in which an antenna is integrated, and FIG. 2B is a sectional view thereof. Referring to FIG. 2A, an antenna 202 is integrated on the top layer of the package and has a spiral shape. Meanwhile, as shown in FIG. 2B, the above-described conductors 204 and 206 for power and ground are disposed below the antenna 202. In this case, the power and ground conductors 204 and 206 negatively influence the antenna 202 in such a way that an electric field and a magnetic field are induced on the conductors 204 and 206, and thus eddy current is generated.
Therefore, in order to decrease the influence between the conductors 204 and 206 and the antenna 202, a structure in which magnetic material, such as a ferrite 208, is interposed between the antenna 202 and the conductors 204 and 206 has been proposed. However, a package having such a structure is also problematic in that the operating characteristics desired by the antenna cannot be exhibited in simulation and measurement, and the size of the package is increased.
FIGS. 3A and 3B are views showing comparison results obtained through the simulation of the influence on the antenna in a conventional RFID reader SiP, in which the antenna is integrated.
FIG. 3A illustrates magnetic flux density distribution, which is the result of the simulation of an antenna in a free space, and FIG. 3B illustrates magnetic flux density distribution obtained when a metal plane is disposed below the antenna.
When the antenna is disposed in a free space, as shown in FIG. 3A, it can be seen that the magnetic flux density is regularly distributed above and below the antenna. However, when the metal plane is disposed below the antenna, as shown in FIG. 3B, the antenna on the metal plane is influenced by the metal plane, so that the magnetic flux density is strongly distributed only in the direction in which the metal plane is placed, and thus the characteristics of the antenna, which must have excellent radiation characteristics, are deteriorated. That is, it can be seen that, when an antenna is integrated in a package, a conductor plane placed below the antenna very negatively influences the operating characteristics of the antenna.
Therefore, a package design method for preventing an influence from being exerted on an antenna that is integrated in the package, as a result of the design itself of the package, is required, in addition to the insertion of magnetic material, such as a ferrite.